1. Field of the Invention
The present invention relates to plug connectors, and more particularly to a plug connector for connecting a printed wiring board to a card-edge connector.
2. Description of the Related Art
It is a conventional practice to provide a printed wiring board with an electrical connection by directly inserting it to a card-edge connector arranged on a motherboard, etc., as disclosed in Japanese Patent Application Laid-open No. 5-074526 (1993). The printed wiring board has a connector-contact arrangement where contact electrodes (hereinafter, referred to as “pads”) are provided as external terminals on the main and back surface thereof so that it can be clamped between a pair of elastically-deformable contact electrodes provided on the card-edge-connector side. This places the pads arranged on the main and back surfaces into electrical connection with the corresponding contact electrodes of the card-edge connector.
In the meanwhile, signal exchanges increases between the printed wiring board and the motherboard, etc. with the increase of processing functions, the number of pads increases on the printed wiring board. Consequently, where the number of pads increases, the distance between the adjacent pads, i.e. pitch, is limitedly reduced, thus resulting in a connector-contact arrangement not narrowed for the printed wiring board. However, the connector-contact arrangement of the printed wiring board has a width regulated related to the card-edge connector, and hence cannot be broadened unlimitedly.
In order to cope with the increasing pads, it is possible to contemplate a connection scheme that a plurality of levels of connector-contact arrangements are vertically provided for one printed wiring board so that those can be inserted to a plurality of card-edge connectors, as shown in FIG. 16, for example.
In FIG. 16, reference numerals 510, 520, 530 . . . are printed wiring boards. In FIG. 16, first and second printed wiring boards 510, 520 have vertical two levels of connector contact regions 511, 512 and 521, 522, respectively. A third printed wiring board 530 is of the usual type having one connector-contact arrangement integrally. Reference numeral 600 refers to a card-edge connector group provided on the side of a motherboard or the like, which has a plurality of card-edge connectors 611, 612, 621, 622, 631 . . .
In the first printed wiring board 510, of the two connector-contact arrangements, the first connector-contact arrangement 511 arranged lower in level is formed integral with the first printed wiring board 510. Meanwhile, the second connector-contact arrangement 512 arranged upper in level is connected with the first printed wiring board 510 via a connector 515. The first printed wiring board 510 is to be electrically connected with a mother board or the like by simultaneously inserting its two connector-contact arrangements 511, 512 to the corresponding card-edge connectors 611, 612, respectively. The second printed wiring board 520 also has a second connector-contact arrangement 522 being connected with the second printed wiring board 520 via the first connector-contact arrangement 521 and connector 525 formed integral with the second printed wiring board 520, similarly to the first printed wiring board 510.
FIG. 16 shows the printed wiring board arranged with the connector-contact arrangements in two levels. However, for certain number of pads, it can be contemplated to insert a multiple levels of connector-contact arrangements to the corresponding card-edge connectors in the case where three levels or more of connector-contact arrangements are arranged for one printed wiring board or in the case where a plurality of printed wiring boards each having a plurality of connector-contact arrangements including one level are combined.
When inserting the connector-contact arrangement to the card-edge connector, the connector-contact arrangement is required to first abuts against a pair of elastically-deformable contact electrode of the card-edge connector and to thereby deform those. For this reason, the connector-contact arrangement is chamfered at its front end thus being structured to reduce the resistance in deforming the contact electrodes of the card-edge connector. However, the printed wiring board is made of epoxy resin in its insulating region. By chamfering the printed wiring board after fabrication, resins or glass fibers are surfaced out. Therefore, the surface chamfered is rough and high in frictional coefficient.
FIG. 17 shows a change in the inserting force, at line (a), required to insert a printed wiring board having one connector-contact arrangement as in the third printed wiring board 530 shown in FIG. 16. As shown by the line (a) in FIG. 17, the inserting force gradually increases as the elastically-deformable contacts of the card-edge connector opens along the slant surfaces of the printed wiring board. Then, the inserting force attains its peak immediately before the contacts reach the upper and lower surfaces of the printed wiring board. Once the contacts reach the upper and lower surfaces of the printed wiring board, the inserting force becomes nearly constant. In this case, the inserting force at the peak is 60 N (approximately 6 kgf). It can be therefore known that at least 60 N of force is required for insertion.
Where simultaneously inserting a plurality of (four, assumed in the figure) levels of connector-contact arrangements to the card-edge connectors, 240 N (approximately 24 kgf) is required as shown at line (b) in FIG. 17. Taking account of a limit of 120 N (approximately 12 kgf) in manual insertion, there is a difficulty in manually inserting the printed wiring board directly to the card-edge connectors. Thus, it can be understood that trouble is possibly encountered in exchanging the printed wiring board.
In order to reduce the inserting force, it can be considered to arrange a plurality of levels of connector-contact arrangements with longitudinal deviations with respect to the inserting direction. With small amount of deviations, nothing is different from simultaneous insertion thus obtaining no or less effect. Conversely, with greater deviations, the connector-contact arrangement or card-edge connector undesirably increases in length. Furthermore, there is a possibility that a plurality of levels of connector-contact arrangements rotate about the front end of the connector-contact arrangement first inserted, resulting in a difficulty in inserting the remaining connector-contact arrangements to the card-edge connectors or in a state similar to that of simultaneous insertion.
Meanwhile, in the connector-contact arrangement, because pads are arranged on the main and back surfaces of the printed wiring board, there is a problem of crosstalk that, when signals are transmitted at high rate, signal leak occurs at between the signal lines connected to the pads.
It is an object of the present invention to provide a plug connector whose inserting force to a card-edge connector required to electrically connect a printed wiring board to a card-edge connector is reduced and which prevents the crosstalk between the signal lines.